Keratoconus is a chronic progressive noninflammatory disorder in which the cornea assumes a conical shape. The corneal thinning induces irregular astigmatism, myopia, and ectasia, leading to a mild to severe decrease in vision quality. It is one of the most common corneal diseases, with a prevalence of 54 in 100,000 and an annual incidence in the general population of 2 in 100,000. Many options for the management of this pathological condition have been described, including corneal collagen crosslinking, fitting a rigid gas-permeable (RGP) contact lens, intrastromal corneal ring segment (ICRS, also known as an intracorneal ring segment) implantation, and lamellar or penetrating keratoplasty.
ICRSs may be implanted through a small surgical incision on the perimeter of the cornea and were originally developed to correct myopia. Several studies report the effectiveness of this surgical technique for improving visual acuity and reducing the refractive error and the mean keratometry (K) value in cases of keratoconus. ICRS implantation may be an effective method to regularize the corneal shape, reducing astigmatism in patients with a clear cornea and contact lens intolerance. The visual and refractive outcomes of this surgery may be highly dependent on the stage of keratoconus.
From a biomechanical viewpoint, the corneal tissue is considered a viscoelastic material that can be modified in response to the presence of a force such as intraocular pressure. In some cases, alterations inside the biomechanical structure found with keratoconus lead to progression of the disease, which has been shown to be more severe during the second and third decades of life. In addition to the benefit of corneal remodeling and improvement in the optical quality of the cornea, some long-term studies report that ICRS implantation may halt the progression of keratoconus.
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